1. Field of the Invention
The present invention relates to a heat exchanger for heat transfer between a first fluid and a second fluid, that includes: a block for the separated and heat-exchanging guiding of the first and second fluid, the block having a plurality of flow channels through which the first fluid can flow; at least one box which is assigned to the block and which is flow-connected to the flow channels; and at least one base, which is provided with one or more through openings for feeding through the flow channels between the block and the box. Whereby at least one through opening is formed as a passage with a collar. The invention relates further to a use of the heat exchanger and to a manufacturing process.
2. Description of the Background Art
Heat exchangers, particularly in mobile applications, are generally made as tube-corrugated fin systems. The block of such a heat exchanger of the aforementioned type has, e.g., a so-called radiator network of an alternating superposing of tubes and heat-transferring corrugated fins. In the aforementioned case in particular, a heat exchanger is exposed to especially high stochastic alternating pressure and thermal stress. The noted alternating stress is critical for the lifetime of a heat exchanger. The alternating thermal stress in a heat exchanger of the aforementioned type is the dominant type of stress because of the especially high mechanical stress amplitudes resulting in the area of the tube ends. It turned out that there is almost always a nonhomogeneous temperature distribution within the block with a nonhomogeneous thermal expansion distribution assigned directly to it, the latter results in strain in the block. In this case, it is of critical importance that the thermal expansion differences within the block can occur not only in a tube lengthwise direction but as a rule also exist transverse thereto. It has become clear in particular that for the corner tubes of the radiator network, this results in relatively great bending deformations in the area of the base connection with the assigned relatively high stresses. Thus, e.g., along the tube circumference the highest stresses in a flat tube can be found in the area of the transition from the tube narrow side to the tube wide side, i.e., in the area of the corner radii. If stresses at the tube base connections in the area of the corner radii or the transition from the tube narrow side to the tube long side are successfully minimized, this can increase the lifetime of the heat exchanger.
A heat exchanger of the aforementioned type with an improved tube-base connection is illustrated is applications by the applicant, for example, German Patent Applications Nos. DE 197 57 034 A1 or DE 103 43 239 A1, which corresponds to U.S. Publication number 20070000657, and which are all herein incorporated by reference. It is proposed as a concept therein to use inverted passages with a collar oriented toward the radiator network, particularly for mobile applications. Improvement of the force flow by reducing the so-called bottom projection, as it is explained with use of FIG. 1B as half the difference between the tube depth t and base depth T, can be used advantageously thereby to increase the internal pressure fatigue strength.
It is known, for example, from British Pat. No. GB 169,855, to secure tube ends in a heat exchanger in a passage. To this end, GB 169,855 discloses a passage with a collar, which at its end facing away from a base plate has a tooth-like contour formed by tongues, the contour in which a tube end is secured flexibly and resiliently.
The mentioned tongues achieve a local lengthening of the passage and are used to equalize an abrupt change in the section modulus in the area of the tube-base connection, in order to take into account possible suddenly occurring changes in the cross section of a tube. In fact, this results in a more flexible and elastic securing of tubes in the area of the passage—the latter, however, leads only to an overall strain relief of a tube-base connection, without counteracting the specific stresses in the area of the corner radii of the tube-base connection.
Likewise, German Unexamined Patent Application No. DE 33 16 960, U.S. Pat. No. 4,150,556, and Japanese Pat. No. JP 11051592 A, disclose other options for a passage with a step-like, in sections linear collar contour for accommodating a flat tube, which in turn can only achieve an overall mechanical improvement for securing a flat tube.
German Patent Application No. DE 39 10 357 A1, which corresponds to U.S. Pat. No. 5,092,397 discloses a passage which to accommodate a heat exchanger tube has a particular raised collar with an oval profile. To avoid cracks in the collar, particularly at large ratios of the largest diameter to the smallest diameter of the same, the collar in the region of its small radii has a smaller height than in the region of its larger radii. As a result, the tearing of the collar is largely eliminated, without a substantial performance reduction of the heat exchanger, also described therein, having to be taken into consideration. A substantially step-like, in sections linear collar contour is also proposed there. This type of heat exchanger merits improvement particularly with respect to problems arising with an internal pressure change and/or temperature change due to tension- and bending-causing stresses.
Overall, these and other approaches generally have the disadvantage that the aim is a one-sided improvement of thermal shock resistance by a relatively thicker or specially designed contour of the passage and/or its collar. In this regard, the requirements necessary for process-secure fabrication, particularly for rather large radiator networks, relating to the process-secure insertion of heat exchanger tubes into the base, are generally neglected. It has proven advantageous to provide an insertion taper as is disclosed, by way of example, in German Patent Application No. DE 100 16 029 A1. In this case, it turned out that the size of the insertion taper for the tubes in the passage or in the collar is limited by the material thickness of the collar. The attempt to resolve the conflict of goals occurring in practice between the collar thickness minimization, sought for reasons of improved thermal shock resistance, and the insertion taper maximization, desired for achieving the greatest possible process security, in DE 100 16 029 A1 in a first approach is to simply curve the collar outward. This simplified approach, however, disadvantageously results inevitably in a relatively great reduction in the contact area between the tube and base, which in turn leads to loss of strength. This circumstance in particular is still worthy of improvement.
It is therefore desirable to improve the durability in a heat exchanger and to simultaneously improve the conditions for a process-secure automated fabrication.